Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $10.77   3.211%   $11.1158   $11.12   $11.10   $11.10  
  Purchase #2 $64.47   6.347%   $68.5619   $68.56   $68.55   $68.60  
  Purchase #3 $151.49   7.729%   $163.1987   $163.20   $163.20   $163.20  
  Purchase #4 $192.84   7.207%   $206.738   $206.74   $206.75   $206.70  
  Purchase #5 $38.78   5.361%   $40.859   $40.86   $40.85   $40.90  
  Purchase #6 $213.44   9.558%   $233.8406   $233.84   $233.85   $233.80  
  Purchase #7 $167.30   13.162%   $189.32   $189.32   $189.30   $189.30  
  7 purchase totals = $839.09       $913.6340   $913.64   $913.60   $913.60